Cell Division

• What structures in eukaryotic cells contain chromosomes?

  The nucleus
• What are the thread-like structures found in the nucleus of eukaryotic cells called?

  Chromosomes
• What are chromosomes made of?

  Highly coiled strands of relatively long DNA
• How many chromosomes do humans have in their body cells?

  46
• How many pairs of chromosomes do humans have in their body cells?

  23
• How many chromosomes do horses have in their body cells?

  64
• How many pairs of chromosomes do horses have in their body cells?

  32
• Which type of cells in the human body have no chromosomes?

  Red blood cells
• Why do chromosomes appear 'X' shaped in micrographs of cells preparing to divide?

  Because the genetic material has been doubled before cell division
• What are the key features of chromosomes?

  • Made from highly coiled DNA
  • Found in pairs in diploid body cells
  • Number of chromosomes varies by species
  • Appear 'X' shaped during cell division
• How do chromosomes behave during the cell division process?

  • Before cell division, chromosomes replicate their DNA
  • This results in the characteristic 'X' shaped chromosomes
  • The replicated chromosomes (sister chromatids) then separate
  • One set goes to each daughter cell during cell division
• What is mitosis?

  A stage when the nucleus divides
• What is the cell cycle?

  A series of stages in a cell's life
• What happens during the growth phase of the cell cycle?

  The genetic material is doubled
• What are chromosomes?

  Genetic material of the cell
• What are chromatids?

  Strands of duplicated chromosomes
• What happens to chromatids during mitosis?

  They are divided between daughter cells
• What occurs to subcellular structures during the growth phase?

  Their number increases in the cell
• Name two subcellular structures that increase during the growth phase.

  Ribosomes and mitochondria
• What is the process by which cells divide to produce two identical daughter cells?

  Mitosis
• Why must cells divide by mitosis in multicellular organisms?

  To allow growth by producing identical cells
• What are the main events that occur during mitosis?

  1. Chromosomes replicate into X-shaped structures
  2. Chromosomes line up along the cell's equator
  3. Chromatids are separated to opposite ends
  4. New nuclei form around each group of chromosomes
  5. Cytoplasm and cell membrane divide (cytokinesis)
• What shape do chromosomes take after replication during mitosis?

  X-shaped chromosomes
• What are the two 'arms' of the X-shaped chromosomes called?

  Chromatids
• Where do the chromosomes line up during mitosis?

  Along the equator of the cell
• What happens to the chromatids during mitosis?

  They are separated and pulled to opposite ends
• What forms around each new group of chromosomes after mitosis?

  A new nucleus
• What is the process called that divides the cytoplasm and cell membrane?

  Cytokinesis
• • So, if a human cell with 46 chromosomes in 23 pairs needs to divide by mitosis:
  • Its 46 chromosomes are doubled, so that there are two copies of each of the 46 chromosomes (or 92 chromatids) in total in the cell
  • The number of ribosomes and mitochondria subcellular structures also increases
  • During mitosis, the chromatids are pulled apart, with a complete set of 46 chromosomes in 23 pairs moving to each end of the cell
  • The cytoplasm and cell membrane divide, forming two new daughter cells
• What is the result of cytokinesis?

  Two genetically identical daughter cells
• What is the overall significance of mitosis in multicellular organisms?

  • Allows growth and development
  • Replaces damaged or dead cells
  • Maintains genetic consistency across cells
• Role of mitosis

  • Cell division by mitosis is important in the growth and development of multicellular organisms
  • When a sperm cell fertilises an egg cell in human reproduction, the resulting zygote cell that forms divides by mitosis, with each subsequent cell produced dividing in the same way to form an embryo
  • As the embryo continues to grow in size, with the cells dividing by mitosis (and differentiating), a fetus forms
  • Therefore, for a multicellular organism to grow, cells have to divide by mitosis to produce an increase in cell number
• What are multicellular organisms made from?

  More than one cell
• How many cells make up a human body?

  Trillions of cells
• What is the purpose of specialised cells?

  To perform a specific function
• How do specialised cells form?

  Through a process known as differentiation
• How many specialised cell types are there in the human body?

  About 250 specialised cell types
• What happens when a specialised cell divides by mitosis?

  Daughter cells are the same type of specialised cell
• What ability do specialised cells lose after differentiation?

  The ability to differentiate into other types of cell
• How does the process of differentiation affect a cell's function?

  It allows the cell to perform a specific function